My goal in these Frequently Asked
Questions is to clarify some popular misconceptions, and I provide
reference to DOT, CGA, or accepted and approved industry standard to
support my answers. This
section of the Graveyard Diver website
is updated frequently as new questions arise, or as
regulations and
standards change. Please check back often. If you
have a
question that you think belongs here, eMail or text Me at the
phone number below.

I
was told that if I repaint my SCUBA cylinder that it would
fail a
visual inspection (or that it is "illegal" to repaint a cylinder).This
is false. Repainting a SCUBA cylinder does not
"automatically"
condemn it IF it is done properly. Cylinder inspectors are
taught
to be suspicious of a repainted cylinder as customers often repaint
cylinders to try to hide repairs or defects. Sometimes a
customer
paints a cylinder and uses methods that damage the cylinder and cause
it
to be condemned. If you bring a repainted cylinder to me, I
will
inspect it according to PSI-PCI guidelines and it may pass a visual
inspection or it may not, depending on how it was repainted and what
chemicals and methods were used to repaint it. Chapter 19,
page
115 of the PSI-PCI "Inspecting Cylinders" manual explains how to
properly repaint your SCUBA cylinder. If you are considering
repainting your cylinder, contact me and I will answer your questions
about how to do it properly without damaging it.

I was told that if I repaint my SCUBA
cylinder that it would have to be re-hydro'd before it could be filled.This
is false. There is no requirement under DOT regulations or
PSI-PCI standards to requalify a repainted cylinder. A dive
shop
may refuse to fill your cylinder if the fill station operator feels
that is some damage you have caused that might affect the integrity of
the cylinder, but repainting alone does not require a cylinder to be
requalified.

The dive shop scraped off all
of my cool dive stickers when they inspected my cylinder.This
is proper procedure for visually inspecting a cylinder.
Sometimes
customers attempt to hide cylinder defects by covering them up with
stickers.
Sometimes water gets trapped underneath stickers and
accelerates
corrosion. Inspectors who properly inspect cylinders will
remove
stickers so that they can perform a thorough inspection. For
a proper
cylinder visual inspection, the entire surface of the cylinder must be
visible to the inspector. Chapter 9, page 62 of the of the
PSI-PCI "Inspecting Cylinders" manual addresses stickers...."The inspector is
obligated to clean away whatever hinders his view." and "Cylinders shall be clean for
inspection to permit the interior and exterior surfaces to be clearly
observed. " ~ CGA, C-8 (5.1)

I was told that tumbling my cylinder
would require it to be requalified.This
rumor is false and is widely circulated under the pretense that
tumbling a cylinder "removes metal from the cylinder wall therefore
weakening the cylinder wall." While it certainly is possible that
your cylinder can be damaged by tumbling, a skilled cylinder technician
knows
how to properly tumble a cylinder. Since the inspector cannot
see
inside the cylinder while it is being tumbled, skill and experience in
tumbling cylinders is definatley helpful. However, tumbling
in
itself does not require a cylinder by hydrostatically retested before
it
can be filled again. Chapter 9, page 66 of the PSI-PCI
"Inspecting Cylinders" manual discusses cylinder tumbling..."Proper
tumbling does not remove significant quantities of base metal therefore
it is not necessary to have a cylinder hydrostatically re-tested simply
because it was tumbled."

The Inspector told me that my aluminum
cylinder had corrosion inside. Aluminum doesn't rust, so
what's the deal?Aluminum
does not rust, but it does corrode. Corrosion in steel is
called
"rust" and is usually a shade of orange. Corrosion in
aluminum is
called "aluminum oxide" and is a white powdery substance usually seen
on the exterior of an aluminum cylinder. When aluminum
corrosion
is wet, it is called aluminum hydroxide and is usually found on the
inside an aluminum cylinder in the form of a white paste-like
substance.
Aluminum corrosion is a slower process than steel corrosion,
but
it is still a destructive process that can seriously damage your
aluminum cylinder.

The dive shop told me that they can't
fill my cylinder because it is too old.This
is a dive shop "policy" and has no foundation in DOT regulations or
generally accepted industry standards. The oldest
known cylinder still in use is a steel cylinder manufactured in 1908
and it is
still in use by a fire department in the northeast United States.
Cylinders do not have an "expiration date" simply due to age
alone. The oldest cylinder I have personally inspected was
manufactured in 1961, and it was in better condition than many newer
cylinders I have inspected. Many dive shop owners concerned
for
safety often use the "Well, you got your
moneys worth out of it"
excuse to refuse to fill a cylinder. While they are within
their
right to refuse to fill a cylinder for any reason, it is the owners
discretion to determine when he has "gotten his moneys worth" out of a
cylinder. Oddly enough, one local dive shop I frequent still
rents cylinders that, the oldest of which I found was manufactured 47
years ago!

The dive shop
told me that my cylinder had to be visually inspected again before they
could fill it because I breathed it totally empty on my last dive.This
is proper fill station proceedure. Chapter 6, page 42 of the
PSI-PCI "Inspecting Cylinders" manual discusses when a cylinder must be
visually inspected. "A visual
inspection is appropriate when any of the following occurs... Cylinder
completely emptied or burst disk fails."

The
dive shop told me that my cylinder had to be visually inspected again
before they could fill it becuase I had to remove the valve in order to
bring it on the plane to the dive destination.This
is proper fill station proceedure. Chapter 6, page 42 of the
PSI-PCI "Inspecting Cylinders" manual discusses when a cylinder must be
visually inspected. "A visual
inspection is appropriate when any of the following occurs...The valve
is removed."

The dive shop told me that my cylinder
had to be visually inspected again even though my VIP decal isn't
expired.This is proper fill station
procedure. Chapter 6, page 41 discusses when a visual
inspection is required. "The frequency of
inspection is dependent upon usage."
A cylinder VIP decal indicates when your cylinder was last
inspected. Extinuating circumstances, suspicious conditions,
and
other factors may require your cylinder be inspected more often than
once per year.

My VIP decal
expires at the end of this month but the dive shop told me my cylinder
had to be inspected again becuase it was expired.I
suspect
this belief comes from motor vehicle inspections, which usually expire
on the last day of the month of the date punched on the window
sticker. According to Hattie Mitchell, Chief DOT Examinations
and
Regulations Termination, U.S. Department of Transportation, a
VIP
decal expires on the last day
of the month in which it is punched.
Thus, if your VIP decal is punched 11/2019, your cylinder visual
inspection expires on November 30th, 2019.

However, the SCUBA industry accepted standard is that a SCUBA cylinder
VIP decal expires on the first
day of the month
in which it is punched. The general reason for
this is that since we don't punch the "day" on a VIP decal, only the
month and year, the fill station guy has no way of knowing what day
that
cylinder was inspected absent a written report. Most divers
don't
carry the written inspection report around with them in their pocket.
Thus, the SCUBA industry considers a visual inspection decal
to
expire on the first day of the month so as to not inadvertently exceed
the 365-day validity of the cylinder visual inspection.

If
the hydro guy visually inspected my cylinder when he requalified it
last week, why do I have to pay to visually have it visually inspected
again?The scuba
cylinder visual inspection program is not (no
matter what the dive shop kid tells you), law. DOT regulation
requires that a cylinder be visually inspected at each 5-year
hydrostatic requalification. The annual
visual inspection is a SCUBA industry standard that dive shops around
the world have chosen to adopt voluntarily for the sake of increased
safety. There is no law in the United States that requires
you to
have your cylinder visually inspected annually. However, a
reputable dive shop will not fill a cylinder that has not been visually
inspected within the last year. The difference is that the
hydro
guy is peforming a federally
mandated DOT
visual inspection, whereas the
SCUBA visual inspector is performing a SCUBA industry standards inspection.

Let
me give you an example. When I lived in Texas my car had to
be
inspected by a mechanic who was licensed in Texas. He
inspected
my vehicle and put a decal on the windshield. I moved to
North
Carolina with my car four months later. The Texas vehicle
inspection sticker was still valid for another eight months, but not in
North Carolina. When I registered my car in North Carolina,
it
had to be inspected again by a mechanic licensed in North Carolina and
he put his North Carolina sticker on the windshield, even though it had
just passed a safety inspection four months earlier.

The
hydro guy does visually inspect your cylinder when he requalifies your
cylinder
every five years. Both inspections are the same, but under
different programs. Just like the Texas and the North
Carolina
vehicle safety inspections are the same, but only valid in their own
jurisdictions

A scuba shop certainly may, at
their discretion, accept
your hydrostatic inspectors requalification stamp as evidence that a
formal cylinder visual inspection has been done. I haven't found one as of
yet that will.

You talk a lot about PSI-PCI.
What about Cylinder Training Services (CTS)? Is
their inspection program not valid?Again, annual visual
inspection of SCUBA cylinders is an industry safety program voluntary standard, not a mandated law.
The only visual inspection required by law is the visual
inspection at each 5-year hydrostatic requalification.
Therefore
a dive shop chooses what inspection agency they will honor and which
they won't. However, if PSI and CTS are both
teaching to
DOT standards, then the result of a visual inspection done by a PSI
visual inspector and visual inspection done by a CTS visual inspector
should yield the same outcome.

So if there is no law requiring an
annual visual inspection, I can just inspect my own cylinder?I
know I'm going to get some pushback from dive shop owners with
this, but I do provide relevant federal law to support my answer...
Technically
yes, practically no. The SCUBA industry standard
requires that
the annual visual inspection be performed by an inspector who has
formal DOT approved training and who has had that training within the
last three years. Each CTS and PSI visual inspector is
required
to "renew" his training every three years by attending a training
update class. If you own your own compressor and fill your
own
cylinder, you don't have to have an annual visual inspection, only a
visual inspection at the 5-year hydrostatic requalification as mandated
by law. However, no reputable dive shop will fill your
cylinder
if your cylinder has not been visually inspected by a formally trained
inspector from a recognized DOT approved certification course within
the
last year. And if you are filling your own cylinders and
doing
you own "visual inspection" without formal training, you are taking you
life into your own hands and endangering others around you. I certainly hope I'm not on the same
cattle boat with you when your uninspected SCUBA bomb explodes.
173.34(e)(3) Code
of Federal Regulations states, "The
only requirement
in
the Code of Federal Regulations for visual internal and external
examination is at the time of retest (once every 5 years).
Annual
visual inspections are by mutual agreement... scuba cylinder owners
submit their cylinders for annual inspections to individuals known to
have been trained and certified to do annual inspections "
173.34(e)(3) is very plainly
worded and crystal clear.

My dive shop told me that it is
illegal to fill old 6351 cylinders.This
is false. DOT regulations state that cylinders
manufactured
of 6351 alloy are legal to use and safe to fill IF they
pass a
hydrostatic test, pass an Eddy Current test at the time of
requlification, and pass a visual inspection. Most dive shops
refuse to fill older 6351 alloy cylinders due to safety concerns over
sustained load cracking. However this is a dive shop policy and
not a law.
You can read the article regarding use of 6351 alloy
cylinders here.

My dive shop told me they had to
Eddy Current test my steel cylinder.This
is dive shop policy,
not law.
The only cylinders required by
federal regulation
to be Eddy Current tested are aluminum cylinders made of 6351-T6 alloy.
Steel cylinders are not prone to sustained load cracking,
however
some visual inspectors choose to Eddy Current test steel cylinders as
an added safety precaution. While steel cylinders are not
prone
to sustained load cracking, all cylinders are susceptible to cracking.
The Eddy Current test may reveal a crack in the neck of a
steel
cylinder that is too small for even a careful visual inspector to see.If
your dive shop insists on Eddy Current testing your steel cylinder,
they are erring on the side of caution. It is your option, of
course, to decline this additional expense and take your steel cylinder
elsewhere for a visual inspection.

My dive shop told me they had to
Eddy Current test my 6061 alloy aluminum cylinder.Again,
this is dive shop policy,
not law.
The only
cylinders required by federal regulations to be Eddy Current tested are
aluminum
cylinders made
of 6351-T6 alloy. Cylinders made from 6061 alloy are not
prone to
sustained load
cracking and thus an Eddy Current test is not required by law.
However, the industry standard recommends that 6061
alloy cylinders be Eddy Current tested to detect possible cracks in the
neck area that are so small that they may be overlooked by even a
careful cylinder visual inspector. So while 6061 alloy
cylinders
are not required by federal
regulation to be Eddy Current tested, it is recomended by
the SCUBA
industry standard to be Eddy Current tested.
If
your dive shop insists on Eddy Current
testing your 6061 alloy aluminum cylinder, they are erring on the side
of caution.
It is your option, of course, to decline this additional
expense and
take your 6061
alloy aluminum cylinder
elsewhere for a visual inspection. "Eddy
current inspection of 6061 aluminum alloy cylinders at the time of the
5 year hydrostatic retest or
annual visual inspection in the case of
SCUBA cylinders is
not required by the U.S.
Department of Transportation (DOT) or the Canadian agency Transport
Canada (TC). Catalina Cylinders
does not require eddy current inspection of the threads of their 6061
aluminum alloy cylinders."
~www.catalinacylinders.com/faqs/current-inspection.

My dive shop refused to put
Nitrox in my cylinder because I didn't have a big ugly yellow and green
Nitrox sticker on it.This
is standard dive industry safety practice. Your dive shop is
adhering
to recognized and accepted industry safety standard. The
Compressed Gas Association states, "SCUBA
cylinders shall not be filled with EANx unless they have been properly
prepared for EANx use. This includes marking the cylinder for EANx
service. EANx cylinders must be conspicuously marked as to
the
specific gas mix (oxygen percentage) inside."

and...

My dive shop refused to put
regular air in my cylinder unless I scraped thebig ugly yellow and
green Nitrox sticker off first.This is standard dive industry safety
practice and federal regulation.
Your dive shop is adhering to recognized and accepted
industry safety
standard. The Compressed Gas Association states, "SCUBA
cylinders shall not be filled with EANx unless they have been properly
prepared for EANx use. This includes marking the cylinder for EANx
service. EANx cylinders must be conspicuously marked as to
the
specific gas mix (oxygen percentage) inside."
Furthermore, 49 CFR 178.65(i)(a) states "a stamped or marked cylinder can
only contain (or be filled) with the gas for which it is stamped or
marked.
" So your dive shop is correct when if refuse to fill your
cylinder with air when you have a Nitrox decal on it.

So
is it a "cylinder" or a "tank"? What's the difference?
A
"cylinder" is a portable vessel that can be removed and is
transportable by the user. A "tank" is a vessel that is
permanently affixed and is not transportable by the user. For
example,
the LP gas vessel used on most forklifts is a "cylinder". It
is
mounted on the rear of the forklift with bands. When it
becomes
empty it is removed from the forklift and refilled, or the empty LP
cylinder is simply removed from the forklift and replaced with a full
one.
My father has an RV that runs on LP gas. The fuel
"tank" is permanently mounted to the frame of the RV. When it
becomes empty, It is not removed for filling or
replaced.
He has to drive the RV to the LP station and have it filled
with
LP gas in the same manner that you fill your car with gasoline.
The pressurized vessels we wear on our backs for SCUBA are "cylinders",
not "tanks". In
the SCUBA industry, "cylinder"
and "tank"
are often used interchangeably. However, formally, there is a distinct
difference.

Can
you visually inspect my old 6351 alloy aluminum cylinder?
Unfortunately,
no. Under current CGA and accepted SCUBA industry safety
standards, all 6351 are required to pass
an Eddy Current test at each annual visual inspection.
Graveyard
Diver does not have a Visual Plus Machine and is not certified to do
Eddy Current testing. If you have a 6351 aluminum alloy
cylinder,
we recommend Divin Dawgs SCUBA in New
Bern. They will be happy to visually inspect and Eddy Current
test your 6351 alloy cylinder.

Why
don't you get certified and buy a Visual Plus Eddy Current test machine
then?
Graveyard
DIver feels that the costs associated with a $1,500+ machine, the cost
of periodic recalibration of that machine required by DOT, and the
expense of the certification class is not a good investment since 6351
cylinders are being gradually "phased out" of service. While
it
is still legal and safe to use and fill 6351 cylinders, they
are
no longer manufactured due to sustained load cracking, and within a few
years 6531 alloy cylinders will be very rare. Graveyard Diver
just feels it is not cost effective for us to invest thousands of
dollars to inspect the few 6351 cylinders that occasionally show up and
that
will probably no longer exist in SCUBA service in a few years

Somebody
told me it was illegal for you to condemn my cylinder.
Sort
of - kind of - but no....173.34(e)(3) Code of Federal Regulations
states that only a person licensed to do hydrostatic requalification
(RIN) may condemn a cylinder..."A
person who only performs visual inspections on DOT or ICC specification
cylinders is not required to obtain a retester identification number.
However, a
compressed gas cylinder may only be rejected [condemned] by a person
who has obtained such a
retester identification number." Since
SCUBA cylinder visual inspectors are not required to obtain a RIN from
DOT, they can't reject (condemn) your cylinder under 172.34(e)(3).
But here's the catch...
When you request a cylinder visual inspection from Graveyard
Diver, or any formally trained inspector, you will complete a form
called a "Visual Inspection Release"
wherein you
agree that should your cylinder fail to meet DOT safety regulations,
you consent to Graveyard Diver condemning your cylinder. In
part,
the release form states, "Should
your
cylinder fail our formal and documented visual safety inspection, it
will be condemned. After required codes and threads have been
obliterated, as a conspicuous disabling measure, the cylinder and valve
will be returned to you. " Your signature on
this release form gives the visual inspector written permission to
condemn your cylinder.
So
the truth of the matter is, it is illegal for a visual inspector who
does not have a RIN number issued by DOT to condemn your cylinder unless you give him
permission to.

Why don't SCUBA cylinder visual
inspectors get a "RIN" number from DOT then?Requalifier
Identification Numbers (RINs) are issued to trained and certified
individuals who hydrostatically test cylinders in a licensed test
facility. A RIN is not required under 173.34(e)(3) for
simply
visually inspecting a cylinder. Of course, a visual inspector
could
qualify for and be issued a RIN from DOT, but it is not
required
by DOT and the expense and recordkeeping requirements are very
extensive. Chances are very good that the cylinder visual
inspector at your local dive shop does not have a RIN if your shop does
not do 5-year hydrostatic requalifications on SCUBA cylinders.

Why
do I have to have a visual inspection on my brand new,
just-got-it-in-the-mail-yesterday SCUBA cylinder? It's brand
new
from the factory!
Believe it or not, SCUBA cylinders do
come from the factory sometimes defective. In the United
States,
SCUBA cylinder manufacturers don't inspect each and every cylinder as
it comes off the assembly line. DOT permits manufacturers to
do "sampling".
In sampling, a quality control employee inspects every ten
cylinders. If a defect is found, he then goes back and
inspects
the previous nine to make sure there are no defects. It is
simply not cost effective to take the time to inspect every single
cylinder that rolls of the assembly line. It is simply more
cost
effective for a manufacturer to possibly have to destroy 9 defective
cylinders than to slow the production line down to impractically slow
speeds. So sometimes, albeit very very rarely, a
cylinder
with a defect can elude the quality control inspector at the plant.
As a prudent safety precaution, your cylinder is visually
inspected by a formally trained inspector even if it is brand
new.

Two years ago, I ordered a pony bottle for a
customer. FEDEX delivered it to me. I opened the
cardboard
box, tore off the plastic bag, and inspected it. The cylinder
had
a valley in the neck area causing the threads not to meet the
safety requirements of DOT for that cylinder to be used in SCUBA
service.
Had that cylinder been filled without a fornal inspection,
the
valve would have likely blown off during it's first fill, possibly
seriously injuring or killing the fill station employee and bystanders.
This
is the reason we inspect brand new cylinders before they are put into
SCUBA service. Every cylinder manufacturer in the U.S. has a
warranty on their cylinders. Although the customer was disappointed in
the delay of his pony bottle delivery, Catalina replaced the
pony
bottle at no charge and the customer received a cylinder that was
perfect and safe to use.

So
whats "Sustained Load Cracking" and why does it only happen in 6351
alloy aluminum cylinders?
Sustained load cracking is a phenomenon
where cracks form in the neck area of 6351 alloy aluminum cylinders
because of the migration of metal in the alloy. 6351 alloy
contains lead. Lead is a soft metal.
Steel cylinders
do not contain lead and 6061 alloy aluminum does not contan lead, so
they are not susceptible to sustained load cracking.
Sustained
load cracking differs from stress cracking becuase sustained load
cracking is a crack opening formed by movement of the metal
whereas stress cracking is formed by seperation of the metal.
So while all cylinders are susceptible to stress cracking,
only
6351 alloy aluminum cylinders are susceptible to sustained load
cracking. Stress cracks usually happen in a short time.
Sustained load cracking does not happen instantly.
It takes
time, often years, for the migration of the lead in the cylinder alloy
to move, or "creep" and form a sustained load crack. The
reason
Eddy Current testing is federally mandated on 6351 alloy aluminum
cylinders is becuase the Eddy Current test can detect the very slow
creep of the metal before
it becomes catastrophic. With 6061 and steel cylinders,
stress
cracks can happen instantly, so there is no preventative measure to
detect those cracks. The diagram below may help you to better
understand sustained load cracking.

Aluminum
6351-T6 alloy consists of nine different metals, the softest being
lead. At the time of manufacture, the molecules
in the Aluminum 6351-T6 alloy are fairly evenly distributed and the
cylinder is able to hold the pressure of the compressed gas.

Over the span of time, as the immense pressure inside a SCUBA cylinder
"pushes" against the molecules of the alloy, the
softer
lead molecules migrate away from the force of the pressure, towards the
exterior of the cylinder wall. Since the other metals
are harder, they do not move as much, but where the lead molecules
congregate, the cylinder wall becomes weaker.

Over a period of years, more and more soft lead molecules are pushed
away, or "creep", from the force of the pressure towards
the
outside of the cylinder wall. Eventually, the cylinder wall
becomes too weak in that area to hold the pressure inside the
cylinder
until BOOM! an explosion occurs from the pressurized
gas escaping through the opening.

The dive shop told me they
couldn't fill my cylinder with nitrox because my cylinder wasn't oxygen
clean.
Your
dive shop was following accepted industry safety standards
As you should have learned in your SCUBA certification class, "regular"
air that we breathe from our SCUBA cylinders consists of 21% oxygen.
No special cleaning of your cylinder is required for regular
air.
However, as the percentage of oxygen increases, the danger of
ignition increases. The
percentage of Nitrox requiring an
oxygen clean cylinder varies among dive shops depending on which
organization's threshold they choose to follow. Most (but not
all) dive shops follow the PADI recommended practice that any Nitrox
mixture of 40% oxygen or greater requires your cylinder to be oxygen
clean. However, some dive shops may follow other agencies
recomendations. Here are some other agencies oxygen cleaning
thresholds:

PSI-PCI:
23.5%

Luxfer:
23.5%

OSHA:
40%

NASA:
21%

Catalina:
23.5%

NOAA:
40%

US
Navy: 25%

NFPA:
21%

PADI:
40%

CGA:
23.5%

ASTM:
25%

Thus,
if your dive shop follows PADI or NOAA standards for oxygen cleaning
thresholds, they probably won't fill your cylinder with Nitrox over 40%
oxygen content unless your cylinder is oxygen clean. If they
follow PSI, Luxfer, or Catalina oxygen cleaning thresholds, they may
require your cylinder to be oxygen clean if you request a Nitrox blend
over 23.5% oxygen. Regardless of which organizations standard
they follow, any reputable dive shop will require your cylinder to be
oxygen clean if they fill your cylinder with Nitrox using the
partial pressure blending method.

My
steel cylinder has "+" stamped on it. My hydrostatic
requalifier
told me that is is illegal for him to restamp a "+" on my cylinder
after the first requalification.
This is false. Steel
cylinders may be requalified to be filled to 10% over their rated
service pressure at any time during their service life and stamped with
a "+" by a qualified hydrostatic inspector, assuming they pass required
testing. Your hydrostatic requalifier may choose not to do
this
extra step, but many do. If you are unable to locate a
hydrostatic requalifier in your area that will requalify and mark your
steel cylinder for 10% over fill, and you can deliver your cylinder to
PSI, they will requalify it and stamp it with the "+" authorizing it to
be filled to 10% over it's rated service pressure. Exception:
Pressed Steel cylinders manufactured under the Special Permit
number 9791 do not use the "+" and may not be filled beyond service
pressure under DOT regulations.

Can
I request my aluminum cylinder to be stamped "+" so it can be filled to
10% over it's rated service pressure?
No.
Aluminum cylinders never qualify for the "+" stamp and may
not be
stamped "+" at requalification. Any aluminum cylinder bearing
a
"+" must be condemned and removed from service.

How
thick is the wall of my cylinder?
I
get this question quite often from customers who are curious.
Cylinder wall thickness varies by manufacturer and type of
material. Steel cylinder walls are generally between 4 to 5
millimeters thick. The walls of aluminum cylinders have to be
thicker because aluminum is a softer metal. Aluminum cylinder
walls are generally 10 to 15 millimeters thick.

Wall thickness of a standard
AL80 aluminum cylinderWith a penny used for
comparrison.

What do you do with cylinders that
do not pass a visual inspection?
Under
DOT regulations and SCUBA industry safety standards, a cylinder that
does not pass a visual inspection based on DOT standards is condemned
and may no longer remain in service. After your cylinder is
stamped "CONDEMNED" and disabled so that it can no longer hold
pressurized gas, it will be returned to you. Customers with
condemned cylinders often sell them for aluminum scrap.
Creative
customer sometimes make cool things from them.